Poly(isobutylene-co-isoprene), or IIR, is a synthetic elastomer commonly known as butyl rubber which has been prepared since the 1940's through the random cationic copolymerization of isobutylene with small amounts of isoprene (1-5 mole %). As a result of its molecular structure, IIR possesses superior air impermeability, a high loss modulus, oxidative stability and extended fatigue resistance.
Butyl rubber is understood to be a copolymer of an isoolefin and one or more, preferably conjugated, multiolefins as comonomers. Commercial butyl comprises a major portion of isoolefin and a minor amount, usually not more than 2.5 mol %, of a conjugated multiolefin. Butyl rubber or butyl polymer is generally prepared in a slurry process using methyl chloride as a diluent and a Friedel-Crafts catalyst as part of the polymerization initiator. This process is further described in U.S. Pat. No. 2,356,128 and Ullmanns Encyclopedia of Industrial Chemistry, volume A 23, 1993, pages 288-295.
Halogenation of butyl rubber produces reactive allylic halide functionality within the elastomer. Conventional butyl rubber halogenation processes are described in, for example, Ullmann's Encyclopedia of Industrial Chemistry (Fifth, Completely Revised Edition, Volume A231 Editors Elvers, et al.) and/or “Rubber Technology” (Third Edition) by Maurice Morton, Chapter 10 (Van Nostrand Reinhold Company© 1987), particularly pp. 297-300.
The presence of allylic halide functionalities allows for nucleophilic alkylation reactions. It has been recently shown that treatment of brominated butyl rubber (BIIR) with nitrogen and/or phosphorus based nucleophiles, in the solid state, leads to the generation of IIR-based ionomers with interesting physical and chemical properties (see: Parent J S, Liskova A, Whitney R A, Resendes R. Journal of Polymer Science, Part A: Polymer Chemistry 43, 5671-5679, 2005; Parent J S, Liskova A, Resendes R. Polymer 45, 8091-8096, 2004; Parent J S, Penciu A, Guillen-Castellanos S A, Liskova A, Whitney R A. Macromolecules 37, 7477-7483, 2004). The ionomer functionality is generated from the reaction of a nitrogen or phosphorus based nucleophile and the allylic halide sites in the halogenated butyl rubber to produce a ammonium or phosphonium ionic group respectively. The physical properties of these halogenated butyl based ionomers, such as green strength, modulus, filler interactions etc., are superior to those of their non-ionomeric counterpart.
Butyl rubber production produces small amounts of cyclic oligomers as side products. Such cyclic oligomers may be undesirable in certain applications of butyl rubber, for example in pharmaceutical seals, closures, medical devices and food grade applications, therefore a reduction in cyclic oligomer levels in the butyl rubber may be desirable. Furthermore, such cyclic oligomers may themselves find utility in certain applications such as precursors for the production of lubricants and traction fluids, therefore obtaining the cyclic oligomers themselves may also be desirable.
It is known from U.S. Pat. No. 7,071,292 and European Patent Publication EP 2610296 that solutions of nitrile rubber and other elastomers in an organic solvent may be purified by ultrafiltration methods. Impurities removed by these processes include emulsifiers, organic and/or inorganic salts or acids such as fatty acids and resins, water, unreacted initiator residues and/or decomposition products, stabilizers, molecular weight regulators, monomers, processing agents, such as flocculants, oligomeric components with a molecular weight of less than 2000 g/mol and transition metal catalysts for the hydrogenation or metathesis, oxidizing and/or reducing agents and/or components of these transition metal catalysts, oxidizing and/or reducing agents preferred impurities are fatty acids, fatty acid esters and Na, K, Ca salts of fatty acids, or resin acids, stabilizers, flocculants water, catalyst components, and ligands.
There remains a need for a method of separating polyisoolefin elastomers, especially butyl rubber, from other components of a polyisoolefin elastomer solution, preferably while retaining sufficient levels of stabilizers in the polyisoolefin elastomer.